RIP Ninja

[Allyrion]

I'm curious as to what this still even does. We know we're getting something to combo off Gust Slash to extend Huton, but they showed two new combat skills in the trailer... I'd assume the very Ninja-y looking ability was Triple Attack, but one of these skills hasn't really been explained.

The triple attack is explained as basically a buff to the next weaponskill move (not a weaponskill in itself). I think the move at 2:58 is the Triple attack (Musou Sandan).
The move following it is a new weaponskill as well as the last move that you linked specifically.

One of these moves is Issou which increases weaponskill damage. The other extends Fuuton.
We don't know which is which though. I can't really guess.